US drug-maker Pfizer has agreed to pay 491 million dollars to settle a probe into illegal marketing of a drug by Wyeth, a firm it had acquired in 2009. The case revolved around Rapamune, a drug prescribed to prevent rejection of transplanted kidneys.

It was alleged that sales staff of Wyeth encouraged doctors to prescribe it for other organ transplants, which were not approved by regulators. Pfizer stressed the illegal marketing occurred before it acquired the firm.

Pfizer was not a subject or target of this matter, and cooperated fully with the government from the time it learned of this investigation in October 2009, the company said in a statement.

The US Department of Justice said: Wyeth trained its sales force to promote Rapamune for off-label uses not approved by the FDA, including ex-renal uses, and even paid bonuses to incentivize those sales.

This is not the first time that Pfizer has had to settle a dispute surrounding Wyeth. Last year, it agreed to pay 55m dollars to settle charges that Wyeth promoted its heartburn drug Protonix for unapproved uses.

The latest settlement comes as Pfizer reported that its earnings more than quadrupled during the second quarter. The firm made a net profit of 14.1bn during the period, compared with 3.2bn during the same period a year ago.